Natalie Portman is wrapping the first of three new Star Wars movies in London- -and preparing a return to New York for her Broadway debut. But the actress, breathtakingly beautiful and all of 16, has more important things to think about.

On a rare day off, she's treating a visiting school friend and a theater-camp chum to fancy breakfast at the Lanesborough, opposite Hyde Park, while she, waif -thin, sticks to yogurt with wheat germ. Afterward, Natalie's mother will shepherd the trio to Harvey Nichols for a healthy dose of English shopping. "I like Helmut Lang, Miu Miu, Abercrombie & Fitch, and I'm a real lipgloss girl, " Natalie exclaims. "And I love Kiehl's!"

And then Natalie, ponytail swinging and looking coltish in a favorite Lang three -quarter-length T-shirt and straight-leg pants, is going to take them all to meet the cast of the first of three eventual prequels to Star Wars--which just happens to include some requisitely good-looking boys. Although Liam Neeson, who plays a Jedi Master, may be out of their league and over their heads ("he's like a friendly giant," Natalie says), Ewan McGregor, playing the young Obi-Wan Kenobi, is the current cute-guy god to young girls.

But it's not stardom or entertaining friends or buying clothes or even cute boys that really weighs on Natalie's young mind. It's homework.

"I work so hard in school," she sighs,"and this is junior year--the year that really counts for college. That's what I'm most nervous about. Normally, I get home after track practice, have dinner for 15 minutes, then do five hours of homework every night. This year, I'm taking more difficult classes: honors physics, math theory, French honors, Japanese II.

"And then I'll be performing every night [she's starring in a new production of The Diary of Anne Frank, which will open on Broadway in December]. I probably shouldn't have taken such hard classes, but I have to be prepared for whatever I might do the rest of my life."

You'd think the girl Hollywood's deemed "the next Audrey Hepburn" since her screen debut at 13 in Luc Besson's The Professional would have the rest of her life fairly well mapped out already. Besson cast her from among many young actresses because of her freshness and fearlessness, combined with an almost other-worldly beauty. Her romantic comedic follow-up in Ted Demme's Beautiful Girls, in which she out-twinkled both Uma Thurman and Lauren Holly, only made her furture in the firmament more secure.

But Portman, born and raised in Jerusalem and now residing in a nice North Shore Long Island town with her doctor father and doting mom (who's also her manager), is a little afraid stardom might mess with her well-honed values.

"I'm not religious," she admits. "But I speak fluent Hebrew and even dream in Hebrew when we visit there, once or twice a year. I have strong feelings about my people and my country. We don't even belong to a temple; it's more about a sense of patriotism. There's not a lot of feeling of patriotism in the States anymore."

To separate her movie-star life from real life, she drops "Portman" (a stage name) and uses her real family name--her parents' name--in her public school and on her passport. It gives her a small amount of anonymity, and a certain reality check that even at 16--in fact, especially at 16--she feels she needs.

"I see relationships in and outside the business," she says, "and inside the business, people are very romantic and sweep you off your feet. Then, two months later, they treat you like you're unimportant. And there are marriages like that !"

"Actors have weird lives," she says with a shrug. "When they're not working, they sleep till three and go to clubs all night. I'm trying to realize how weird it all is, because sometimes, when you're around that all the time, it becomes normal. I have such a different image from my parents, who are so in love, and are very pure people: They don't do drugs, they don't drink. I like being in and out of the business. It's fun getting dressed up and going to parties. It's also fun going home to my dog and my house."

Then again, she's not averse to flirting with the wild world of modeling. Portman was discovered by a Revlon scout in a Long Island pizza parlor when she was 13, and finally appeared as a model in last year's "Isaac" campaign for Isaac Mizrahi, shot by Dewey Nicks. She loved it, loved Isaac, got to keep a few outfits ("hardly anything fits me 'cause I'm so small"), but then turned down Miu Miu and several other lines to concentrate on keeping her tiny feet on the ground.

Swinging London, meanwhile, has not impressed her. "Everyone's been saying London's exploding, how cool it is, the coolest stores, the coolest everything," she says. "But I don't think the people who've been saying that have ever been in New York. People in New York know how to have fun. People in London think fun just means one thing: getting drunk. They know all the hangover cures here."

But not most of the Star Wars troupe. They worked five very long days a week there, because of all the special-effects shooting, upping that to six when they moved to locations in Tunisia.

"This is the first job job I've had," she says. "Every other acting job was more like playing. I play Princess Leia's mother, and I have 10 different looks. So I woke up at six in the morning and got home at 9:30 at night. In Tunisia, it was over a hundred Fahrenheit--the locals don't even go out during the day--and we worked from 3 a.m. to 5 p.m."

Still, The Diary of Anne Frank is the project she's yearned to do the longest. "I read the book when I was 12, and ever since then, I've been looking for some kind of Anne Frank project to do. When I heard James Lapine was directing it for Broadway, I thought it was perfect.

"Anne was 16 when she wrote about her experiences. You know, when we were in Tunisia, they did random passport searches at the border, and my passport says I was born in Jerusalem. They'd take my passport and not come back for 15 minutes, and my heart would stop. I felt like I was in Nazi Germany!"

Portman managed to juggle her intensified junior-year class schedule to take on the production, an adaptation of Frances Goodrich and Albert Hackett's play (which won a Tony and a Pulitzer) by playwright and screenwriter Wendy Kesselman, that includes new material from the 1995 version of the diaries. The cast of The Diary (Anne Frank includes Broadway veterans Harris Yulin, Linda Lavin, Austin Pendleton and George Hearn, which makes Broadway naif Portman breathe a sigh of relief.

"At first, they were going to get all film actors, but I'm glad they turned out to be experienced theater people," she says. "I've always been so afraid of forgetting my lines--that's why I haven't done a play. Last summer, at theater camp in the Catskills, we put our plays together in three weeks. So I figured, if I could do that, I can do this. It might be more stressful to be in a play with all kids."

Portman has been as remarkably mature about the film roles she's turned down as those she's taken. She was signed to play Kristin Scott Thomas' daughter in The Horse Whisperer when it was meant to start shooting, under Robert Reclford's direction, two years ago. When the movie stalled, she suggested the part should go to someone younger, since the character's 13-and the commitment would have interruped the Anne Frank schedule.

She also turned down Lolita, even though director Adrian Lyne begged her to play the nymphet, even promising a body double for nude scenes (the part eventually went to Dominique Swain). Lyne never had a chance, since it was Natalie, not her parents, who deemed the project "sleazy"--or so she said in several interviews. Her foresight seems 20-20: the movie, even with Jeremy Irons in it, has been unable to get a U.S. distributor.

"I think I was misquoted," she says with a grin. "But so many press people were so intrigued with why I passed on it. Maybe because it's so sexual. Well, my parents let me make my own judgments about films. They let me do The Professional, and that was also controversial.

"But they also know I'm very conservative. My mom was telling me the other day, 'I wish you were a little more outgoing with the way you dress.' I dress very conservative: skirts to the knee, three-quarter-length sleeves, little coats. It's not true that skinny people can wear anything. Besides, I'm not that skinny."

She deals with her incredible beauty the way only a few beautiful people do- -with a kind of learned, well-mannered modesty.

"I've never really thought about being beautiful," she muses. "It's not that I'm insecure--I might look at a picture of me and think it's a beautiful picture. But believe me, I can take awful pictures, too. I've just tried not to concentrate that hard on looks. I care what I look like, but eventually, looks fade. I know that's a cliche, but it's true. Sometimes I think people who are not attractive have it easier," she adds, "because when they get older, they've really developed the other parts of themselves--their personalities, their intelligence."

Portman doesn't know whether to attribute this beyond-her-years wisdom to her parents, her schooling, her extensive travel or the experience of having made six movies (including Mars Attacks, Heat and Everybody Says I Love You). But now that major directors and famous actors are treating her like an adult--almost like an equal--she's not so sure she likes it.

"People used to be so careful not to curse around me, or drink," she says, laughing. "Now, it's expected that I'm going to be 'mature.' Do you know, in England, when you're 16, you don't need a guardian? Over here, you don't have to live with your parents when you're 16, and you can leave school if you want.

"Could you imagine me living on my own? My Mom and I shared a house in Primrose Hill all summer, and my dad came almost every weekend. I've been thinking I'm going to try to get more independent this year. Maybe I'll do my own laundry, and even iron, so I'll be more ready for college."

Portman is already pondering an application to Harvard and other major schools. She scored a 1320 combined on her PSAT test, excelled in math and science and is trying to figure out some avenue that might allow her to be an actress part-time and still pursue a more fulfulling career.

"I'd love to be a veterinarian," she says, "but I can't imagine being able to pull off being a doctor and an actress. Maybe I could be a writer and an actress. But I don't know if I'd be able to deal with just acting, because I don't know if you get to use your brain that much. You do, for certain roles, but not most. Acting is more of a hobby for me."

Portman takes pride in the reality that most of her friends aren't in show business. She loves Liv Tyler, whom she met auditioning for Little Women, and she keeps in touch with her. But as for the other young girls with exceptional lives like hers--Claire Danes, Kate Winslet, Christina Ricci--she says she has no need to seek them out.

"I don't feel like I have an exceptional life," she says. "I'm just doing what I like. I feel a bond with people who are like, my friends. Y'know? Not with people with lives like mine.

"People with exceptional lives sometimes turn out to be boring. What happens to a lot of child actors is, they're precocious and they know it. So when they get older, that's when they get immature. If everyone's so impressed with you when you're younger, you'll probably never change. So I'm hoping I'm not gonna be that way--because I've caught on to that."